PET/MRI in the Diagnosis of Hormone-Producing Pituitary Microadenoma: A Prospective Pilot Study

This study was designed to evaluate the ability of PET/MRI, using ¹⁸F-FDG and ⁶⁸Ga-DOTATATE as tracers, to detect hormone-producing pituitary microadenoma when diagnosis is difficult using MRI alone. Methods: We recruited 37 patients with elevated hormone levels, including 19 with undiagnosable primary pituitary adenoma and 18 with suspected recurrent pituitary adenoma. ¹⁸F-FDG PET/MRI and ⁶⁸Ga-DOTATATE PET/MRI were performed within 1 wk of each other in all patients. Within 2 wk afterward, 27 of the 37 patients underwent transsphenoidal adenomectomy, 3 underwent sella region radiotherapy, 1 underwent somatostatin therapy, and 6 had only clinical follow-up. The image characteristics and uptake levels were correlated with the surgical findings and pathologic results. Receiver-operating-characteristic curves were analyzed to determine the optimal cutoff to differentiate adenoma from normal pituitary tissue. The area under the receiver-operating-characteristic curve was calculated to compare diagnostic performance. Results: The PET/MR images were of diagnostic quality and without obvious image artifacts. The high contrast of the PET images provided complementary information to the fine anatomic display of the MR images. Increased ¹⁸F-FDG uptake was clearly observed in all patients. MRI enhanced using a 0.05 mmol/kg dose of gadopentetate dimeglumine showed suggestive findings in only 47% of the patients with primary adenoma and 39% of those with recurrent adenoma; when a 0.1 mmol/kg dose was used, the respective percentages were 37% and 50%. The ¹⁸F-FDG SUVmax of the 16 primary adenomas that underwent transsphenoidal adenomectomy (6.8 ± 3.7) was significantly higher than that of normal pituitary tissue (3.2 ± 1.1, P < 0.01). The adenomas showed moderate ⁶⁸Ga-DOTATATE uptake (SUVmax, 3.8 ± 2.6), but the ⁶⁸Ga-DOTATATE uptake was generally lower than that of normal pituitary tissue (SUVmax, 6.2 ± 3.2, P < 0.05). In the 11 suspected recurrent pituitary adenomas that underwent transsphenoidal adenomectomy, the ¹⁸F-FDG SUVmax was 6.1 ± 3.5, significantly higher than that of normal pituitary tissue (2.5 ± 1.1, P < 0.01), and the ⁶⁸Ga-DOTATATE SUVmax was 3.0 ± 1.1, significantly lower than that of normal pituitary tissue (5.5 ± 1.7, P < 0.01). The ¹⁸F-FDG/⁶⁸Ga-DOTATATE SUVmax ratio of the adenomas (2.3 ± 1.5) was significantly higher than that of normal pituitary tissue (0.6 ± 0.3, P < 0.05). When the ¹⁸F-FDG SUVmax alone and the ¹⁸F-FDG/⁶⁸Ga-DOTATATE SUVmax ratio were used as criteria to discriminate between adenoma and pituitary tissue, the best analysis came from the ratio, and that from ¹⁸F-FDG SUVmax alone was slightly less, with optimal diagnostic cutoffs of 1.04 and 3.88, respectively. Conclusion: PET/MRI provides an ideal tool for the detection of hormone-producing pituitary microadenoma. Dual-tracer ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/MRI was useful for distinguishing pituitary microadenoma from normal pituitary tissue.